function HHI = HHI_fun(market_share)

HHI = market_share(:,1).^2 + market_share(:,2).^2 + market_share(:,3).^2+ market_share(:,4).^2+ market_share(:,5).^2 + market_share(:,6).^2   ...
      + market_share(:,7).^2 + market_share(:,8).^2 + market_share(:,9).^2 ;
